Dealing with Tomato Diseases

GROW — practical gardening tips

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Tomatoes, alas, are not the easiest vegetable to grow. Here in the midwest and most of the U.S.A. our growing season is not long enough, so we have to buy seedlings and transplant them into our gardens. In addition, weather conditions and pests cause other problems. Just look at the “common issues” that the Bonnie Plants website lists with many of its tomato plants, even with its “super disease resistant” varieties:

Common issues: Plants may stop setting fruit when temperatures dip below 55˚ F or climb above 90˚ F. Blossom end rot can be a problem, as can misshapen fruit.

I remember fondly my early years of gardening when I was a stranger to all these common issues. If you are still in that situation, count your blessings and garden on! But don’t be naive about it—do everything you can to prevent fungal and bacterial diseases from starting in your garden. Once they come, they overwinter in the soil and keep coming back.

Here is a rundown of what I do to prevent soil-borne diseases on my tomato plants and to keep them from spreading once they make their inevitable appearance.

  1. Water from below—never spray water onto the foliage. This, by the way, is a good rule to follow for all plants. You always want to water their roots, not the leaves. Many other plants are also susceptible to fungal diseases that are spread by overhead watering. I use soaker hoses in my raised beds. Whenever I use the regular hose for watering, I attach a long water wand to it so that I could direct the water down toward the roots without bending over.
  2. Mulch to prevent rain from splashing soil up onto the plants. Years ago I used sheets of red plastic in my beds. Then I got Tomato Craters, the round red plastic things around the bottoms of my tomato plants which everyone always asks me about. These hold up better from year to year and give me more flexibility in placement of the plants. There are similar products available now which work better at directing water down to the root zone, called Tomato Automators and Tomato Halos or Plant Halos. I also use mulch in my container tomatoes.
  3. Rotate crops. I have six raised beds for rotating my vegetable plants, and I usually fill two of them with tomatoes and other nightshades like peppers, eggplants, and tomatillos. That gives me the minimum 3 years of rotation. 5-7 years would be better, but I’m not ready to cut down to just one bed of tomatoes yet.
  4. Space plants farther apart to improve air circulation. I do space my tomatoes further apart than I used to, but I never got to the minimum ideal of at least 4 ft. apart in all directions. I get fairly close to that in my 4’x10′ raised beds by planting four tomatoes on each side for a total of eight in each bed. I used to plant three more tomatoes down the middle, but in 2021 I switched to planting a row of bush beans down the middle of my tomato beds instead; they are good companion plants. I also put two celery plants between the tomatoes. Intercropping like this makes good use of the room created by spacing the tomatoes farther apart, and it also cuts down on weeds in the bed. And because I can’t stand the thought of growing fewer tomatoes, I began growing even more tomatoes in containers.
  5. Prune plants well. Removing suckers improves air circulation. Removing the lower branches prevents fungal spores from splashing up from the soil onto the leaves. Unfortunately, I tend to put this off until I see a fungal disease already beginning to affect the lowest leaves. Maybe next year I will finally do this earlier!
  6. Remove diseased leaves as soon as possible. I tend to get diseases that work their way from the bottom of the plant up. As I noted above, removing the lower leaves prevents rain from splashing the fungal spores up onto the higher leaves. In order to prevent my clippers from spreading the disease from plant to plant, I spray them with Lysol before moving on to the next plant. I used to use rubbing alcohol because a bleach solution is corrosive to tools and requires a ten-minute soak to be effective. Then I found a study which showed that Lysol is more effective than alcohol.
  7. Spray the plants with an organic fungicide with copper in it, such as Bonide, or with Bacillus subtilis in it. I prefer the latter and have had the best success with a Bayer product called Serenade, which is apparently no longer available. Next time I will try Monterey Complete Disease Control or Grower’s Ally Fungicide. Again, I tend to put this off until I see the disease beginning each year, so I’m writing this post as a reminder to myself as well as instructions for you. It would be better to start soon after I set the plants out since I know my garden is susceptible.
  8. Clean up! Clean up! Clean up! Remove the plants and as much of their debris as possible at the end of the season. Turn over the soil and try to bury anything left. We always add composted manure to the raised beds. Clean and disinfect the cages and other staking tools. I’ve always been careful to wash the Tomato Craters, and I usually leave the cages outdoors in sunlight and rain to sanitize them. Sometimes I spray or wipe them down with Lysol, too.

Those are my recommendations for dealing with fungus and bacterial diseases in tomatoes. If you find yourself dealing with fungus and bacterial soil borne diseases every year, there is one more option that you may want to try. When planting tomatoes next year, you could apply a root protection drench, such as Bioworks Rootshield or Gardens Alive Root Guardian. I had great success with the latter the first time I tried it, and Gardens Alive put my glowing review in their catalog and on their website. Unfortunately, the next year they sold me some that was too close to its expiration date and it was ineffective. It has a very short shelf life and is rather expensive. I then switched to the Bioworks product, but the next year’s rainy spring made it a bad year for my tomatoes even though I’d done my best to get fresh product and apply it properly. I have not tried it since.

This post, a follow-up to an earlier post, Fight the Blight, was updated in 2022. If you found it helpful, please share it! You may also leave a reply below to let me know how your tomatoes are doing. Stay tuned for future developments in my ongoing fight against tomato diseases.

Published by Debbie Rea - The Gardener Wife

Helping you to GROW SOMETHING, something beautiful—even better, something to eat! Speaker, Writer, and Influencer—available for speaking engagements on gardening and/or Christian faith topics and for collaborations on home and garden products

3 thoughts on “Dealing with Tomato Diseases

  1. Thank you for sharing your expertise and experience, and for the practical things I can do to grow better tomatoes. I checked out the tomato bases, and the Tomato Crater looks like it’s the best bang for the buck. I’m afraid I’m also guilty of waiting until the spots start before I take action…the tomato plant in the picture looks just like mine last year! I will try to do better this summer as well. Looking forward to a bigger and better crop!


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